The present invention relates generally to frame synchronizers for establishing synchronization between a high speed TDM (time division multiplex) signal and demultiplexed low speed signals.
In frame synchronizers, low speed digital signals are multiplexed into a high speed TDM signal to achieve a high level of utilization of channel resources and transmitted to a distant end where it is decomposed by a demultiplexed into the individual components. The low speed signals are usually multiplexed in units of a byte length into a frame and a sync pattern is inserted at the beginning of each frame. In a prior art system, a frame synchronizer is provided at the input port of the demultiplexer to detect the sync pattern to control the demultiplex timing so that the low speed signals appear at proper output ports of the demultiplexer. This frame synchronizer first establishes synchronism with the incoming high speed TDM signal using the inserted sync pattern, and then proceeds to decompose the synchronized signal into the low speed components. However, the recent tendency toward using TDM signals at a speed in the range between several hundred Mbps and several Gbps makes it difficult to implement a frame synchronizer capable of operating in this speed range.